Radio receiving instrument for systems of broadcast distribution



E. E. CLEMENT RADIO RECEIVING INSTRUMENT FOR SYSTEMS OF BROADCAST DISTRIBUTION Filed June 18, 1924 2 Sheets-Sheet 1 40 3 z I I m j; z w 2 1 TE Z E 2W Dec. 11, 1928. 1,695,174

E. E. CLEMENT RADIO nscmvme INSTRUMENT FOR SYSTEMS OF BROADCAST DISTRIBUTION Filed June 18, 1924 2 Sheets-Sheet 2 311021 How Patented Dec. I1, 1928. V

UNITED STATES I 1,695,174 PATENT OFFICE.

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Application fled June 18,

My invention relates to subscribers" station circuits and apparatus for combined telephone and radio telephone systems in which current is supplied to the radio-tele- 8 phones as well' as the telephones over a common system of wired lines.. It has for its object to render the supply of energy to the subscribers radio-telephone constant whether his telephone .is in use or not, and I is in the nature of an improvement over the invention described and claimed in my prior copending applications Serial No. 681,829, filed August 14, 1922, Patent No. 1,522,357, granted Janua 6, 1925, and Serial No. 699,023, filed arch 13, 1924. Where'the usual centralized battery is employe in a telephone system, a constant potential is maintained on the lines, and'when the telephones are not in use, the radio-telephones can be ad'usted so as to function properly on the telep one current, using the metallic circuit onl without substation grounds; but it is esirable to compensate for the change in potential when a telephone trans- 2 mitter of low resistance is bridged across the line, especially with respect to' the filament current taken over that line. As dis-' closed in the earlier of thetwo applications referred to, a cut ofi relay is provided at the subscribers station, which becomes energized when the telephone is in use, to disconnect the normal charging circuit from the line to the radio telephone storage battery. In the second application a bridged arrangement of both instruments is resorted to, the plate and filament circuits being in parallel, with resistance interposed in the filament circuit. In the present case I employ a combination of the principles thus disclosed, using bridging circuits without grounds, and compensating resistance which willautomatically regulate the voltage and the current in the filament circuit when the telephone is in use.

Other objects will sufliciently appear from the detailed description hereinaften.

My invention is illustrated in the accompanying drawings, in which Fig. 1 is a diagram of a subscribers station containing a telephone and a radio telephone receiver, with common battery supply over the line from a central office, and automatic compensating resistance device associated with the radio telephone.

Fig. 2 is a side view of a telephone desk 1924. Serial no. 720,870.

stand showing a fixed switchhook mounted thereon to hold the radio telephone receiver,

and also showing elements of the radio telephone housed in the base of the desk stand.

F g. 3 is a diagram similar to Fig. 1 show ng a modified circuit in which a fixed compensating resistance is em loyed, with a relay in the telephone circult, acting to cover and uncover said resistance according to the condition of use or disuse of the telephone.

Fig. 4 is a similar diagram of'another modification showing a variable compensating resistance, and a controlling relay therefor similar to that shown in Fig. 3.

Fig. 5 is a similar diagram showing the same compensating resistance as in Fig. 4, but with the controlling relay bridged and pperatingas a potential relay across the Referring to Fig. 1 of the drawings, 1 and 2 are line wires leadin from a telephone central ofiice to the tefiephone subscribers station T. At the central office end of'the line suitable terminals are supposed to be '80 provided, and a bridged"source of'current shown as a battery B feeding into'the line through typical choke coils bb. The

usual voltage in manual telephone exchanges is 22. The usual voltage in automatic telephone exchanges is 50, where electromagnetic switching is relied upon, and in the prcsent'case all the circuits shown and described have been tested on voltages ranging from 22 to 50, with entire success. Unless otherwise stated, however, in this application the battery B may be assumed to deliver from 22 to 25 volts at its terminal. It need scarcely be said that the choke coils b-b are individual to the lines whenever the battery busses are connected thereto, these coils representingeither cord circuit relay or repeating coil or choke coil units, or line relay windings normally included when the line is not in telephoneuse. Under all condi- 1 tions, a steady flow of current not exceeding 350 milliamperes maybe assumed as within good practice, over the ordinary telephone lines, including paper cables. A larger current than this can be drawn through ordinary lines up to say 1 half ampere, without violatin the underwriters requirements, but in suc case special provision must be made for preventing operation of the ordinary sneak-current or no heat coil arresters, which are usually set at not to exceed 350 milliamperes for a limited time. The tube V employed in the radio telephone set shown in Fig. 1 is supposed to take only 60 milliamperes in its filament circuit, and a negligible amount in its plate circuit. As a matter of fact, when the tests were made on these circuits, the best results were attained with a filament current not exceeding 50 milliamperes.

Bridged across the wires 1-2 is the telephone T, having a transmitter t, a receiver r, switchhook h, supplemental hook h, carrying the radio telephone receiver 1", a ringer 1' and a Qmf condenser C. Extending from the telephone terminals to the radio tele hone set are wires 3-4.. WVire 3 goes to t 1e primary of the induction coil. I, from which wire 5 extends to the tickler coil 6 and thence to the plate p of the detector tube V. It should be stated that wire 1 goes to the positive or plus side of battery B and wire 2 to the minus or negative side; hence the connection of the plate p of the subscribers vacuum tube is correct, being to the positive side of battery. Wire 3 is also connected to wire 5 through a compensating resistance 8-8 to the filament rheostat wk of the tube V. The filament f is connected on its other side to the wire 9 and thence back through wire 4 to the No. 2 or negative side of line. The compensating resistance s-s is controlled by means of plunger core a working in the solenoid S, which is included in series in the filament circuit, The

connections are such that the larger the current in the circuit the more resistance is automatically uncovered by the rise of the plunger 3 the smaller the current below normal the less resistance will be included. Thecoil S has a secondary function, in that it ofi'ers impedance and thereby chokes any sudden rise of current in the filament circuit, which might otherwise flash and damage the filament before sufficient resistance could be cut in to protect it.

On its input side, the tube V has its grid circuit connected as usual through a grid condenser and a grid leak to the secondary coil 71 of the coupler coil I connected to the antenna circuit 7-8. G is the tuning condenser for the antenna circuit, and C the corresponding condenser for the input circuit.

The operation of this circuit of Fig. 1 is as follows: Through an ordinary line of approximately 1 mile to 1 miles long, the potential available at the telephone terminals is from 18 to 20 volts, which is suiticient for the radio telephone circuits, both plate and filament, using a detector and telephone head set only. With the telephone in the position of disuse as shown in the drawing, the full voltage and full current supplied over the line are available for the radio telephone. If the telephone receiver 7' is taken down for use, however, during use of the radio telephone, it will be ob.- served thata direct bridge of low resistance is put across the line byway of the wire 1, winding 11 of the induction coil I, switchhook h, and telephone transmitter t. This draws enough current from the line to cause a decided drop in potential, which must be compensated for, especially in the filament circuit of the radio telephone. In Fig. 1 this is done by means of the resistance s8 regulated in the flow of current in the solenoid S. When the potential drops, the current flow becomes smaller, the core 8 falls and the resistance in the filament circuit is cut down. When the telephone receiver is again hung up, and the telephone circuit is opened, full voltage will be restored to the wires 3-4, and there will be a rise of current in circuit 5, ss', S and f. The resulting energization of coil S will allow the core 8 to cut in more resistance, and at the same time will automatically choke the rise of current to protect the filament.

Fig. 3 contains substantially the same elements and functions in substantially the same manner as the circuit of Fig. 1, except that the compensating resistance in this case is a fixed resistance Na, in series with the choke coil 6' in the filament circuit 5*. This compensating resistance M. is covered or-shunted-when the telephone is taken off .the hook by means of relay R whose windings are included in series witlr'the telephone transmitter t, and whose armature when pulled up closes the local short circuit 5 In order that the windings of R shall not oifer undue impedance to the voice waves originated in transmitter t, I provide a shuntingcondenser C of ample size for low or voice frequencies, as for example 2mf.

Referring to Fig. 4, substantially the same circuit is shown therein as illustrated in Fig. 3, the controlling relay B being in series with the telephone transmitter and shunted by a talking condenser; the compensating resistance r72? having taps taken oil and connected to contacts of a switch 8 by which the amount of resistance cut in or out by therelay B may be regulated. In this figure the telephone parts are simplified, the switchhook being shown as a small manna switch for convenience.

- Fig. 5 shows a modification of the circuit in Fig. 4, in which the controlling relay R has its windings bridged directly across the line wires 1-2. The relay R in the precedlng figures, being a series relay, is low wound, but in the case of the relay R which is a bridging relay, it is necessary to make its windings of very high resistance, as for example 2500 ohms or even higher. A

switch S is provided by means of which the circuit of relay R and the circuit of the tube filament f may be closed and opened. The relay opens and closes a shunt around the resistance rh and Th, as before, and it will be noted that as this relay lets go, when the telephone is taken down for use, its armature closes on a back contact, while the armature of the corresponding relay in Fig. 4 closes on the front contact. In other words, the relay R of Fig. 4 pulls up on current in the telephone transmitter circuit; while the relay R in Fig. 5 is shunted by the telephone transmitter circuit and lets go its armature.

What I claim is:

1. In a combined telephone system and radio telephone system, a pair of line wires, a central ofiice source of current supply for said line wires, a subscribers telephone connected to said line wires, a subscribers radio telephone also connected to said line wires,

means for supplying current from said central source to either or both of said instruments over the line wires, and automatic means for regulating the .amount of current supplied to one instrument when the other is in use, said regulating means being directly responsive to changes in current flow due to change inrelative resistance in the two instrument circuits and acting thereupon to produce a compensatin change in the resistance of the radio telep one circuit.

2. The system described in claim 1 in which the regulating means consist of a solenoid relay having a moveable core, and a rheostat adjustable by said core in its movement, said rheostat and the windings of said solenoid being included in series 1n the current supply circuit of the instrument to be regulated.

3. The system described in claim 1 in which the re ulating device is a relay adapted to vary t 0 amount of resistance in the current supply circuits of the radio telephone, and having the fiow of current in its own windings determined in the use of the telephone.

4. The system described in claim 1 in which the regulating device includes a relay adapted to have its current sup ly varied when the telephone transmitter is bridged across the line, and an adjustable rheostat controlled thereby.

5. The system described in claim 1 in which the regulating device includes a relay adapted to have its current supply varied when the telephone transmitter is bridged across the. line and arranged to adjust a variable resistance in proportion to the current in the relay winding.

6. The system described in claim 1 in which the regulating device includes a relay adapted to have its current supply varied when the telephone transmitter is bridged across the line, and adapted to cover and uncover resistance in the radio tele hone circuits to compensate for the drop ue to the bridging of the said transmitter.

7. A combined telephone and radio telephone instrument c'omprising a desk standard and base, a telephone transmitter and receiver connected to said desk standard, a movable switchhook adapted to support the receiver and operable by the weight thereof to open and close the telephone circuits, and radio telephone receiving apparatus including a vacuum tube mounted inside the base of said desk standard, together with a rheostat for said vacuum tube and an opening through the base to expose the tube from without, whereby the rheostat may be adjusted and the effect therefor will be visible to the operator.

In testimony whereof I hereunto aflix my signature.

EDWARD E. CLEMENT. 

